The invention provides sheeting articles having a retroreflective layer with upper and lower surfaces and a luminescent layer disposed upon the upper surface of the retroreflective layer. The invention also provides articles such as signs made from the sheeting.
Retroreflective materials are generally known for use in applications where high visibility is a necessity, for example in traffic signs and other safety applications. The retroreflectivity of these materials provides for high visibility at night when illuminated by a headlight, flashlight or other light source from the same side of the material as the the viewer of the material, i.e., a xe2x80x9cfront-litxe2x80x9d surface
One type of retroreflective material comprises microspheres of a material such as glass that have a specular reflecting layer coated on one surface to reflect the incident light. An example of this type of retroreflective material is available under the trademark SCOTCHLITE from Minnesota Mining and Manufacturing Company, St. Paul, Minn.
Another type of retroreflective material is made up of cube corner elements. This type of retroreflective material is described in, for example, U.S. Pat. No. 4,588,258 to Hoopman et al. The cube corner elements may be separated, producing flat areas that will transmit light from behind the retroreflective layer. This technique is described in Benson, U.S. Pat. No. 5,122,902.
Luminescent dyes and pigments are also known in the preparation of signs and other articles where visibility in dark conditions is required. Chemiluminescent and/or photoluminescent materials may be used. The luminous material may be attached to exits, stairways, fire extinguishers, and so on to guide a person in the event of a power failure. While this is effective immediately after loss of power occurs, the luminescence of such materials decreases rapidly and may be substantially gone in a relatively short time.
These photoluminescent films are known and are commercially used to provide signage that warns, cautions, and provides other messages conveying safety information. Frequently, these films are combined with an adhesive to form a photoluminescent tape. Sometimes also characterized as xe2x80x9cGlow-in-the-Darkxe2x80x9d, xe2x80x9cluminousxe2x80x9d, or xe2x80x9cluminescentxe2x80x9d, these films or tapes are based on materials that absorb photons and emit visible light.
Photoluminescent films and tapes can be found in commercial catalogs such as the Seton Identification Products Catalog (Seton Products, Branford Conn., page AE33, 1996); DandG Sign and Label Catalog WK (DandG Sign and Label, Northford, Conn., page W37, (Summer 1996); and Brady-Signmark Division Catalog S-17 (W. H. Brady Co., Milwaukee, Wis., p. 46, 1996). Typical messages include xe2x80x9cDangerxe2x80x94High Voltagexe2x80x9d; xe2x80x9cExitxe2x80x9d; xe2x80x9cFire Alarmxe2x80x9d; xe2x80x9cFire Extinguisherxe2x80x9d; xe2x80x9cOxygen No Smokingxe2x80x9d; and the like. Some of the messages include graphics and multiple colors such as the xe2x80x9cDangerxe2x80x94High Voltagexe2x80x9d sign with the xe2x80x9cDangerxe2x80x9d printed in photoluminescent white in a red oval within a black rectangle above xe2x80x9cHigh Voltagexe2x80x9d printed in black within a photoluminescent white rectangle. The messages are prepared using silk-screening or other analog printing techniques.
Thus, it would be desirable to provide a signage article that combines the properties of retroreflectivity and luminescence. An article having such properties would be highly visible when there is a light source available to impinge upon its surface in a xe2x80x9cfront-litxe2x80x9d condition and would also be visible in conditions of complete or near-complete darkness.
Attempts have been made to combine retroreflectivity and luminescence in a signage article. In U.S. Pat. No. 5,243,457 Spencer describes a sheeting material that has a layer of luminescent material behind a layer of retroreflective material. The retroreflective layer used in this sheeting is not transparent or translucent and is said to protect the luminescent layer from decay. In U.S. Pat. No. 5,315,491 Spencer et al. provide a sign made from such a material with backlighting. Zampa, U.S. Pat. No. 5,415,911 provides a multilayered sheeting material that has a retroreflective layer and a phosphorescent pigment in at least one of the layers beneath the retroreflective layer.
In certain situations it may be desirable for a sign to be internally illuminated from the side opposite of the side seen by the viewer so that it may be viewed in the absence of retroreflective lighting conditions, i.e., a xe2x80x9cback-litxe2x80x9d surface. Bradshaw et al., U.S. Pat. No. 4,952,023 describes a sign that is retroreflective and is internally illuminated.
All of the known prior art materials that combine retroreflective and luminescent materials provide the luminescent layer behind or on the reverse face of the retroreflective layer. Such materials are relatively expensive to manufacture and are susceptible to peeling damage because signs that are produced from such materials often have lettering cut from the retroreflective material and adhesively applied to the luminescent layer. For example, the mere peeling of one letter can tremendously change the message conveyed by a sign in a retroreflective environment. xe2x80x9cSTOPxe2x80x9d has a very different message if it becomes xe2x80x9cTOPxe2x80x9d.
Thus, there is a need in the art for a material that effectively and efficiently combines the properties of retroreflectivity and luminescence. Moreover, there is a need in the art of signage to combine the best properties in xe2x80x9cfront-litxe2x80x9d and xe2x80x9cback-litxe2x80x9d signage which employs both retroreflective materials and luminescent materials.
Accordingly, one aspect of the invention provides an article, preferably a sheeting material, having retroreflective and luminescent properties, with a retroreflective layer having an upper surface and a lower surface and a luminescent layer disposed upon the upper surface of the retroreflective layer. This material can be used to prepare signs, labels, and other articles where high visibility under a variety of conditions is required, and such articles are also provided by the invention.
Preferably, at least a portion of the retroreflective layer is exposed through one or more openings in the luminescent layer.
Also preferably, the luminescent layer or the retroreflective layer or both can be made of a material that permits back-lit illumination of the article. Such signs are visible under conditions of external or front-lit illumination and are also visible when there is no external light source, either by virtue of the internal light source or other back-lit source or by virtue of the luminescence itself of the luminescent layer.
Also preferably, the luminescent layer can be imaged by an analog or digital printing process. In this manner, any possible combination of cut and digitally printed image graphics can be created for education, entertainment, information, and the like.
Either or both of the layers can be flexible to withstand bending caused by assembly, usage, or environmental conditions such as high winds.
Any of the preferable options can be combined into various embodiments of the invention, which are discussed in more detail below.
The articles of the invention combine the beneficial properties of retroreflective and luminescent materials, providing visibility both when light is available and in conditions or near or total darkness. These properties are enhanced when at least one of the retroreflective or luminescent layers is translucent, such that some light can pass through the layer.
The term xe2x80x9cluminescentxe2x80x9d is used interchangeably with xe2x80x9cphotoluminescentxe2x80x9d and describes materials that absorb photons and emit visible light.
Further features and advantages of the invention will be discussed with respect to the following embodiments.